bison program.ypp # to create C++ file program.tab.cpp
bison -d program.y # to create header file program.tab.h for lexer
flex program.l
gcc -c lex.yy.c # create the object file lex.yy.o
g++ program.tab.cpp lex.yy.o # compile parser and link lexer 
bison expr.ypp # to create C++ file expr.tab.cpp
bison -d expr.y # to create header file program.tab.h for lexer
flex expr.l
gcc -c lex.yy.c # create the object file lex.yy.o
g++ expr.tab.cpp expr.cpp lex.yy.o # compiler parser and link lexer 
